This invention relates to improvements in the design for downhole equipment used in the completion of petroleum wells. More particularly, it relates to an improved design for a device used to create perforations in the well casing through which oil and gas are extracted from a reservoir.
In most conventional oil and gas wells the well is completed by cementing a string of steel casing in the well across the production zone near the bottom of the hole. Once this casing is in place production of the oil or gas is permitted by perforating holes in the casing opposite the production zone using shaped explosive charges known as a perforating gun.
Perforating guns for this purpose are normally lowered down the hole inside the casing on a cable (with an electrical connection) until the explosive charges are opposite the production zone. The electrical wires are energized to ignite the charges which pierce holes in the casing (and any surrounding cement) into the rock formation and allow the flow of the oil or gas into the well. These techniques are old and well known in the industry.
However, a problem often arises that with the explosion of the perforating charges the gun and attached cables and wires are often explosively driven up the well casing where they become tangled and jammed in the casing bore so that they cannot be removed by merely hoisting the cable. This often requires an expensive and time-consuming "fishing" operation to release the entanglement and retrieve the debris.